The plasma membrane has been suggested to be the site of alterations in excitation-contraction coupling known to occur in arterial smooth muscle of hypertensive subjects, but the mechanisms responsible are not completely understood. the proposed studies are based upon the hypothesis that increased sympathetic nerve activity to blood vessels in hypertension influences the biophysical and pharmacological properties of Ca2+ and K+ channels in the plasma membrane contributing to alterations in excitation- contraction coupling, and that this effect is mediated through changes in the lipid composition and lipid order of the phospholipid bilayer of the plasma membrane. To test this hypothesis, the following specific aims will be addressed using cells and plasma membranes isolated from the thoracic aorta and mesenteric artery branches of 20 week old WKY and SHR.
Aim 1 : To compare the biophysical and pharmacological properties of Ca2+ and K+ channels with plasma membrane lipid (cholesterol and phospholipid) profiles and physical state (fluidity) in WKY and SHR.
Aim 2 : To determine the effect of neonatal sympathectomy (with anti-nerve growth factor and guanethadine) in modulating the relationship between ion channel properties, and plasma membrane lipid profile and fluidity. The biophysical and pharmacological properties of Ca2+ and K+ channels will be determined using whole cell, patch clamp methods. The lipid composition of isolated plasma membranes will be determined with lipid analytical procedures using membranes isolated by differential ultracentrifugation techniques. The fluidity of isolated plasma membrane will be determined from measurement of fluorescence anisotropy using a membrane probe 1,6- diphenyl-1,3,5-hexatriene. A relationship between ion channel properties, and plasma membrane lipid profile and fluidity will be established (Aim 1) by multivariable analysis of variance. The effect of the sympathetic nervous system on these relations will be assessed by peripheral sympathectomy with neonatal anti-nerve growth factor plus guanethidine (Aim 2). This procedure will be compared with the effects of antihypertensive (hydralazine-hydrochlorothiazide-propranolol) therapy (Aim 3) to separate the contribution of reduced arterial pressure to these relationships. The goals of this proposed research are to demonstrate: a) that differences exist in Ca2+ and K+ channel properties between WKY and SHR; b) that these differences are related to differences in plasma membrane lipid profile and fluidity; c) that the sympathetic nervous system modulates this relationship and contributes to the differences in excitation-contraction coupling in hypertension; and d) that the differences are due to an effect of the sympathetic nervous system on plasma membrane lipid composition.
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